Method and apparatus for compensation during ultrasound examination

Abstract

The time-gain function of an ultrasound receiver for medical examinations is modified to compensate for different attenuation characteristics in body structures. The slope of the time-gain function is increased at times associated with pulse transmission through the highly attenuating body wall and may be decreased at times associated with pulse transmission through fluid filled body structures. The time-gain compensation, in combination with probe focus compensation and a highly linear receiver transfer function provides sharply increased diagnostic quality. The location and attenuating characteristics of body structures may be determined from a prior knowledge of their depth within the body or from distinctive signatures in ultrasound echos.

What is claimed is: 
     
       1. A method for processing received signals in an echo ultrasound examination system comprising the steps of: amplifying the signals with a gain controlled amplifier;   increasing the gain of the amplifier as a function of time to compensate for the attenuation of ultrasound energy at varying depths within a body;   identifying characteristic signatures of varying tissue types by measuring the level of scattered echos returned from said tissue types; and   adjusting the rate of the gain variation of the amplifier, in response to said signatures, to compensate for the varying degrees of attenuation attributable to different tissue types.   
     
     
       2. The method of claim 1 wherein highly attenuating tissues are identified with high levels of scattered energy and less attenuating tissues are identified with lower levels of scattered energy. 
     
     
       3. The method of claim 2 wherein the level of scattered energy is determined by comparing the level of scattered echo signals with a predetermined threshold. 
     
     
       4. The method of claims 1, 2, or 3 further comprising the step of adjusting the gain of the amplifier to compensate for focussing effects in a transducer probe. 
     
     
       5. The method of claim 4 wherein the amplifier has a time-gain transfer function which is linear within plus or minus 1 dB over the dynamic working range of the receiver. 
     
     
       6. Apparatus for compensation of an echo ultrasound examination system comprising: a gain controlled amplifier connected to amplify echo signals received from a body;   a time-gain compensation ramp generator connected to control the gain of the amplifier receiver; and   means for identifying signal signatures characteristic of body tissue types having varying attenuation levels in scattered echo signals returned from said tissue types and for controlling the slope of a time-gain compensation ramp produced by said generator in response to the identification.   
     
     
       7. The apparatus of claim 6 wherein the means for identifying comprise one or more threshold circuits. 
     
     
       8. The apparatus of claim 6 wherein the means for identifying identify body wall tissue whenever the level of scattered echo signals exceeds a predetermined first threshold level. 
     
     
       9. The apparatus of claim 7 or 8 wherein the means for identifying identify tissue having low attenuation levels whenever the level of scattered echo signals does not exceed a second threshold level. 
     
     
       10. The apparatus of claim 6 further comprising means which vary the gain of the amplifier to compensate for focussing effects in a transducer probe. 
     
     
       11. The apparatus of claim 6 or 10 wherein the time-gain transfer function of the amplifier is linear to within plus or minus 1 dB over the working range of the receiver.